JP2015114266A - Polarization analyzing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarization analyzing apparatus that can quickly measure polarization characteristic of samples.SOLUTION: A polarization analyzing apparatus comprises a light source 2 that emits light having a prescribed wavelength range, a polarizer 32 that transmits light emitted from the light source 2, a spatial phase modulator 5 that transmits light from a sample S, an analyzer 42 that transmits light transmitted by the spatial phase modulator 5, and an image spectroscope 6 that receives the light transmitted by the analyzer 42. The spatial phase modulator 5 is made of a birefringent material, and the phase difference varies from position to position in a first direction within a plane orthogonal to the optical axis. The image spectroscope 6 splits light in a second direction different from the first direction within the plane orthogonal to the optical axis.

Description

  The present invention relates to an ellipsometer.

  Patent Document 1 discloses a spectroscopic ellipsometer that acquires the polarization state of a sample by a rotating analyzer method.

  Patent Document 2 discloses a Stokes meter that performs sign determination of the Stokes parameter S2 by a phase modulation method using a photoelastic modulator.

JP 2009-103598 A JP-A-5-172644

  However, in the spectroscopic ellipsometer disclosed in Patent Document 1, it is necessary to mechanically rotate the analyzer and detect light at each angle.

  In addition, in the Stokes meter disclosed in Patent Document 2, it is necessary to change the applied voltage of the photoelastic modulator for each measurement wavelength and detect light at each stage when performing spectroscopic measurement. It takes time.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an ellipsometer capable of quickly measuring the polarization characteristics of a sample.

  In order to solve the above-described problem, an ellipsometer of the present invention includes a light source that emits light having a predetermined wavelength region, and a polarizer that transmits light emitted from the light source, the light passing through the polarizer. A polarizer, which is irradiated with light, and a spatial phase modulator that transmits light from the sample, the birefringent material, at each position in a first direction in a plane perpendicular to the optical axis A spatial phase modulator having different phase differences, an analyzer that transmits light transmitted through the spatial phase modulator, and an image spectrometer that receives light transmitted through the analyzer, wherein the optical spectrometer is orthogonal to the optical axis. An image spectroscope for performing spectroscopy in a second direction different from the first direction in the plane to be performed.

  In the aspect of the invention, the phase difference of the spatial phase modulator may continuously change along the first direction.

  In the aspect of the invention, the birefringence difference of the spatial phase modulator may continuously change along the first direction.

  In one embodiment of the present invention, a beam expander that expands a beam diameter of light from the sample and irradiates the spatial phase modulator may be further provided.

  In one embodiment of the present invention, the spatial phase modulator may include two regions adjacent to each other in the first direction, each having a fast axis direction or a slow axis direction different from each other.

  In the aspect of the invention, the analyzer may include two regions adjacent to each other in the first direction, each having a different polarization direction, corresponding to the two regions of the spatial phase modulator. .

  According to the present invention, it is possible to acquire spectral information according to the phase difference in one shot.

It is a figure which shows the outline of the 1st example of an ellipsometer. It is a figure which shows the outline of an example of a light-receiving unit. It is a figure which shows the outline of the modification of a light reception unit. It is a figure which shows the outline of the modification of a light reception unit. It is a figure which shows the outline of an example of a spatial phase modulator. It is a figure which shows the outline of the 2nd example of an ellipsometer. It is a figure which shows the outline of the modification of a light reception unit. It is a flowchart which shows the application to a 1st example. It is a flowchart which shows the application to a 2nd example.

  Embodiments of the present invention will be described with reference to the drawings.

[First example of ellipsometer]
FIG. 1 is a diagram schematically illustrating an ellipsometer 1 according to a first example. The ellipsometer 1 according to the first example is a spectroscopic ellipsometer.

  The ellipsometer 1 includes a light source 2 that generates light to irradiate the sample S, a light projecting unit 3 that irradiates the sample S with the light generated by the light source 2, and a light receiving unit 4 that receives the light reflected by the sample S. And.

  As the light source 2, a white light source having a flat output characteristic in a wide wavelength region is preferable, and a deuterium lamp, a tungsten lamp, or the like may be adopted. The light emitted from the light source 2 has, for example, a wavelength region with a width of at least 100 nm, and particularly preferably has a wavelength region with a width of at least 200 nm. The wavelength region is arbitrarily determined within a region including a near ultraviolet region (about 200 to 400 nm), a visible region (400 to 800 nm), and a near infrared region (about 800 to 1000 nm). For example, the wavelength region may include the entire visible region, may straddle the near ultraviolet region and the visible region, or may straddle the visible region and the near infrared region.

  The light projecting unit 3 is supported so as to be movable in the circumferential direction around the sample S so that the incident angle of light can be changed. The light projecting unit 3 includes a polarizer 32, and light transmitted through the polarizer 32 is polarized into linearly polarized light.

  The light receiving unit 4 is supported so as to be movable in the circumferential direction around the sample S so that the detection angle of light can be changed. The light receiving unit 4 includes a spatial phase modulator 5, an analyzer 42, and an image spectrometer 6.

  FIG. 2 is a diagram showing an outline of an example of the light receiving unit 4. In the light receiving unit 4, the spatial phase modulator 5, the analyzer 42, and the image spectroscope 6 are arranged in this order from upstream to downstream of the light.

  The spatial phase modulator 5 is made of a birefringent material, and is configured such that the phase difference is different at each position in the phase modulation direction PM in a plane orthogonal to the optical axis. The phase modulation direction PM corresponds to the longitudinal direction of the slit 6 a of the image spectrometer 6. The spatial phase modulator 5 transmits light having a predetermined wavelength region generated by the light source 2, that is, white light. The direction of the fast axis and the slow axis of the spatial phase modulator 5 is not particularly limited. For example, the fast axis and the slow axis are set in parallel and perpendicular to the phase modulation direction PM, respectively. Details of the spatial phase modulator 5 will be described later.

  The light transmitted through the spatial phase modulator 5 passes through the analyzer 42 and then reaches the image spectrometer 6. The angle difference between the direction of the fast axis and the slow axis of the spatial phase modulator 5 and the polarization direction of the analyzer 42 is preferably 45 degrees, for example. The angle difference between the polarization direction of the polarizer 32 and the polarization direction of the analyzer 42 is preferably, for example, 0 degrees.

  The image spectrometer 6 includes a grating (diffraction grating) that splits light incident from the slit 6a, and an image sensor in which imaging elements such as a CCD are two-dimensionally arranged. The light transmitted through the analyzer 42 is shaped into a line shape by the slit 6 a and enters the image spectrometer 6. The grating splits the light incident from the slit 6a in a spectral direction SP in a plane perpendicular to the optical axis. The spectral direction SP corresponds to the width direction of the slit 6a and is orthogonal to the phase modulation direction PM. The image sensor receives light having different phase differences at each position in the phase modulation direction PM and having different wavelengths at each position in the spectral direction SP. Thereby, it is possible to acquire spectral information according to the phase difference in one shot.

  An arithmetic unit (not shown) calculates a phase difference Δ for each wavelength, an angle Ψ of an amplitude ratio, and the like by data analysis based on spectral information corresponding to the phase difference acquired by the image spectroscope 6, and finally the film Thickness and optical constants are calculated.

  For example, as shown in FIG. 3, the image spectrometer 6 may include a wavelength tunable filter 67 and an image sensor 69. The wavelength tunable filter 67 modulates the wavelength of light that passes through the wavelength tunable filter 67 so that the wavelengths are different from each other at each position in the wavelength modulation direction WM in a plane orthogonal to the optical axis. The wavelength modulation direction WM is orthogonal to the phase modulation direction PM.

  For example, as shown in FIG. 4, the light receiving unit 4 may further include a beam expander 7. The beam expander 7 expands the beam diameter of the light reflected by the sample S and irradiates the spatial phase modulator 5. The aspect provided with such a beam expander 7 is suitable when the spot diameter of the light irradiated to the sample S from the light projection unit 3 is small.

  FIG. 5 is a diagram showing an outline of an example of the spatial phase modulator 5. The spatial phase modulator 5 includes a retardation film 52 made of a birefringent material, a pair of stretching devices 54 attached to both sides of the retardation film 52, and a controller 56 connected to the pair of stretching devices 54. ing.

  The pair of stretching devices 54 is such that the amount of stretching is relatively small on one side in the width direction (vertical direction in the drawing) of the phase difference film 52 and the amount of stretching is relatively large on the other side. 52 is extended in a fan shape. At this time, the birefringence difference of the retardation film 52 is relatively small on one side in the width direction and relatively large on the other side, and continuously from one side to the other side along the width direction. It has increased. Along with this, the retardation of the retardation film 52 also continuously increases from one side to the other side along the width direction. That is, the width direction of the retardation film 52 becomes the phase modulation direction PM. The retardation film 52 preferably includes a range in which the phase difference changes from 0 to one wavelength (360 degrees) along the phase modulation direction PM.

  The controller 56 adjusts the stretch amount of the retardation film 52 in order to compensate for the temperature dependence of the characteristics of the retardation film 52. Alternatively, the controller 56 may adjust the temperature of the retardation film 52 in order to compensate for the temperature dependence of the characteristics of the retardation film 52.

  The spatial phase modulator 5 is not limited to the above-described aspect. The spatial phase modulator 5 may be an optical component having a structure in which the phase difference changes in one direction as described above.

[Second Example of Ellipsometer]
FIG. 6 is a diagram schematically illustrating the ellipsometer 10 according to the second example. About the structure which overlaps with the above-mentioned 1st example, detailed description is abbreviate | omitted by attaching | subjecting the same number. In the second example, the light projecting unit 3 and the light receiving unit 4 are arranged to face each other, and the light receiving unit 4 receives light transmitted through the sample S.

[Modification of light receiving unit]
FIG. 7 is a diagram illustrating an outline of a light receiving unit 40 according to a modification. In the figure, only the spatial phase modulator 5 and the analyzer 42 included in the light receiving unit 40 are shown, and the illustration of the image spectroscope 6 is omitted. This modification is applicable to both the first example and the second example.

  In this modification, the spatial phase modulator 5 includes two regions 52a and 52b adjacent to each other in the phase modulation direction PM. The direction of the fast axis and the slow axis of the first region 52a is different from the direction of the fast axis and the slow axis of the second region 52b, and the angle difference is, for example, 45 degrees. Is preferred. Double arrows shown inside the two regions 52a and 52b in the figure indicate the direction of the fast axis.

  Similarly, the analyzer 42 includes two regions 42a and 42b adjacent to each other in the phase modulation direction PM. The polarization direction of the first region 42a and the polarization direction of the second region 42b are different from each other, and the angle difference is preferably 45 degrees, for example. Double arrows shown inside the two regions 42a and 42b in the figure indicate the polarization direction.

  The first region 52a of the spatial phase modulator 5 and the first region 42a of the analyzer 42 are opposed to each other, and the light transmitted through the first region 52a of the spatial phase modulator 5 is transmitted through the analyzer 42. The light passes through the first region 42 a and then reaches the image spectrometer 6. The angle difference between the direction of the fast axis and the slow axis of the first region 52a of the spatial phase modulator 5 and the polarization direction of the first region 42a of the analyzer 42 is preferably 45 degrees, for example.

  The second region 52b of the spatial phase modulator 5 and the second region 42b of the analyzer 42 are opposed to each other, and the light transmitted through the second region 52b of the spatial phase modulator 5 is transmitted through the analyzer 42. The light passes through the second region 42 b and then reaches the image spectrometer 6. The angle difference between the direction of the fast axis and the slow axis of the second region 52b of the spatial phase modulator 5 and the polarization direction of the second region 42b of the analyzer 42 is preferably 45 degrees, for example.

  Each of the two regions 52a and 52b of the spatial phase modulator 5 preferably includes a range in which the phase difference changes from 0 to 1 wavelength (360 degrees) along the phase modulation direction PM. Such two regions 52a and 52b are realized, for example, by providing two sets of the retardation film 52, the pair of stretchers 54, and the controller 56 shown in FIG.

  When the light receiving unit 40 according to the modification described above is used, all of the Stokes parameters S1, S2, and S3 can be calculated. Hereinafter, the case where the light receiving unit 40 according to the modification is applied to each of the first example and the second example described above will be described.

  In the following description, the angle of the polarization direction of the polarizer 32 is expressed with reference to the fast axis (see FIG. 7) of the first region 52a of the spatial phase modulator 5.

[Application to the first example]
FIG. 8 is a flowchart showing measurement when the light receiving unit 40 according to the modification is applied to the ellipsometer 1 according to the first example (see FIG. 1).

  In S11, the incident angle / detection angle θ is set to 90 degrees and the polarization direction of the polarizer 32 is set to 45 degrees, and measurement is performed without the sample S. That is, by setting the incident angle / detection angle θ to 90 degrees, the light projecting unit 3 and the light receiving unit 4 are opposed to each other, and the intensity of the light transmitted through only the air between the two is measured by the image spectrometer 6.

  In S12, for the first region 52a (fast phase axis: 0 degree) of the spatial phase modulator 5, from the change in intensity for each wavelength measured by the image spectroscope 6, the phase difference distribution δ is calculated according to Equation (2) described later. Calculate (0-2π).

  In S13, the incident angle / detection angle θ is set to 90 degrees and the polarization direction of the polarizer 32 is set to 90 degrees, and measurement is performed without the sample S. That is, by setting the incident angle / detection angle θ to 90 degrees, the light projecting unit 3 and the light receiving unit 4 are opposed to each other, and the intensity of the light transmitted through only the air between the two is measured by the image spectrometer 6.

  In S14, for the second region 52b (fast axis: 45 degrees) of the spatial phase modulator 5, from the change in intensity for each wavelength measured by the image spectroscope 6, the phase difference distribution δ is calculated according to Equation (2) described later. Calculate (0-2π).

  In S15, the incident angle / detection angle θ is set to 0 degree or more and less than 90 degrees, the polarization direction of the polarizer 32 is set to 45 degrees, and the intensity of the light reflected by the sample S is measured by the image spectrometer 6.

  In S16, the phase difference Δ for each wavelength, the angle Ψ of the amplitude ratio, the Stokes parameters S1 to S3, and the like are calculated according to equations (3), (4), and (5) described later.

  In S17, the film thickness, optical constant, and the like of the sample S are calculated from the phase difference Δ for each wavelength, the angle Ψ of the amplitude ratio, and the like.

[Application to the second example]
FIG. 9 is a flowchart showing the measurement when the light receiving unit 40 according to the modification is applied to the polarization analyzer 10 (see FIG. 6) according to the second example.

  In S21, the polarization direction of the polarizer 32 is set to 45 degrees, and measurement is performed without the sample S. That is, the intensity of light transmitted only through the air between the light projecting unit 3 and the light receiving unit 4 is measured by the image spectroscope 6.

  In S22, for the first region 52a (fast axis: 0 degree) of the spatial phase modulator 5, from the change in intensity for each wavelength measured by the image spectroscope 6, the phase difference distribution δ is expressed by the following equation (2). Calculate (0-2π).

  In S23, the polarization direction of the polarizer 32 is set to 90 degrees, and measurement is performed without the sample S. That is, the intensity of light transmitted only through the air between the light projecting unit 3 and the light receiving unit 4 is measured by the image spectroscope 6.

  In S24, for the second region 52b (fast axis: 45 degrees) of the spatial phase modulator 5, from the change in intensity for each wavelength measured by the image spectroscope 6, the phase difference distribution δ is calculated according to Equation (2) described later. Calculate (0-2π).

  In S25, the polarization direction of the polarizer 32 is set to 45 degrees, and the intensity of the light transmitted through the sample S is measured by the image spectroscope 6.

  In S26, Stokes parameters S1 to S3 and the like for each wavelength are calculated by mathematical formulas (3), (4), and (5) described later.

  In S27, the birefringence phase difference of the sample S is calculated from Stokes parameters S1 to S3 for each wavelength.

[Derivation of Stokes parameters]
Derivation of the Stokes parameters S1 to S3 will be described with reference to mathematical expressions.

  The polarization direction of the polarizer 32 is set to 45 degrees, the angle difference between the fast axis direction and the slow axis direction of the spatial phase modulator 5 and the polarization direction of the analyzer 42 is set to 45 degrees, and the image spectrometer 6 The light intensity I (δ) measured at δ = 0 to 2π is given by the following mathematical formula (1). δ represents the phase difference of the spatial phase modulator 5.

  In the case of no sample S, the above formula (1) is simplified and the following formula (2) is obtained.

  The polarization direction of the polarizer 32 is set to 90 degrees, the angle difference between the direction of the fast axis and the slow axis of the spatial phase modulator 5 and the polarization direction of the analyzer 42 is set to 45 degrees, and the image spectrometer 6 The light intensity I (δ) measured at δ = 0 to 2π is also given by the above equation (1), and when the sample S is not provided, the above equation (2) is obtained.

  The phase difference distribution is obtained from the above equation (2) and used in the following equations (3) and (4). The phase difference Δ of the sample S and the angle Ψ of the amplitude ratio can be obtained from these mathematical formulas (3) and (4).

  With respect to the first region 52a (fast axis: 0 degree) of the spatial phase modulator 5, the above formula (1) becomes the following formula (3), and the phase difference Δ of the sample S and the angle Ψ of the amplitude ratio are plural. Using the light intensity measured at δ, the equation (3) is obtained by the least square method or the like.

  Regarding the second region 52b (fast axis: 45 degrees) of the spatial phase modulator 5, the above formula (1) becomes the following formula (4), and the phase difference Δ of the sample S and the angle Ψ of the amplitude ratio are plural. Using the light intensity measured at δ, the equation (4) is obtained by solving the least square method or the like.

  The Stokes parameters S1, S2, and S3 are obtained from the following equation (5) using the phase difference Δ of the sample S and the angle Ψ of the amplitude ratio.

  When obtaining the phase difference Δ of the sample S and the angle Ψ of the amplitude ratio, the light intensity measured for each wavelength and for each phase is used, so that the phase difference Δ of multiple wavelengths and the angle Ψ of the amplitude ratio are obtained at one time. Can do. According to this, it is possible to improve the measurement accuracy.

  In the conventional rotational analyzer method and phase modulation method, the Stokes parameters that can be calculated are limited, but according to the method described above, all of the Stokes parameters S1, S2, and S3 can be calculated. .

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made by those skilled in the art.

  DESCRIPTION OF SYMBOLS 1,10 Polarization analyzer, 2 Light source, 3 Light projection unit, 32 Polarizer, 4,40 Light reception unit, 42 Analyzer, 5 Spatial phase modulator, 52 Phase difference film, 54 Stretcher, 56 Controller, 6 Image spectroscopy , 6a slit, 67 tunable filter, 69 image sensor, 7 beam expander.

Claims (6)

A light source that emits light having a predetermined wavelength region;
A polarizer that transmits light emitted from the light source, and the sample is irradiated with light transmitted through the polarizer; and
A spatial phase modulator that transmits light from the sample, the spatial phase modulator being made of a birefringent material and having different phase differences at each position in a first direction in a plane perpendicular to the optical axis;
An analyzer through which light transmitted through the spatial phase modulator is transmitted;
An image spectrometer for receiving light transmitted through the analyzer, wherein the image spectrometer performs spectroscopy in a second direction different from the first direction in a plane perpendicular to the optical axis;
An ellipsometer comprising: The phase difference of the spatial phase modulator varies continuously along the first direction;
The ellipsometer according to claim 1. The birefringence difference of the spatial phase modulator continuously changes along the first direction.
The ellipsometer according to claim 1 or 2. A beam expander for expanding the beam diameter of the light from the sample and irradiating the spatial phase modulator;
The ellipsometer according to any one of claims 1 to 3. The spatial phase modulator includes two regions adjacent to each other in the first direction, each having a fast axis direction or a slow axis direction different from each other.
The ellipsometer according to any one of claims 1 to 4. The analyzer includes two regions adjacent to each other in the first direction, each having a different polarization direction, corresponding to the two regions of the spatial phase modulator.
The ellipsometer according to claim 5.

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